This invention relates to an image forming apparatus (such as a copier or a printer) using electrophotographic technology, and more particularly to a developer bearing body used in a developing device of the image forming apparatus.
Conventionally, an image forming apparatus (such as a printer or a copier) is configured to form an image on a recording medium by electrophotographic processes. In a charging process, a photosensitive drum is charged. In an exposing process, a latent image is formed on the photosensitive body according to image data. In a developing process, the latent image on the photosensitive drum is developed (visualized) with toner. In a transferring process, the developed toner image is transferred to a recording medium such as a paper. In a fixing process, the toner image is fixed to the recording medium by means of heat and pressure.
In such an electrophotographic image forming apparatus, the size of a printable pixel is reduced, in order to precisely reproduce an image and to enhance the image quality. For this purpose, a polymerized toner which is uniform in shape and size (and therefore suitable for enhancing the image quality) is recently used as a developer, instead of a pulverized toner which is nonuniform in shape and size and has a broad distribution of charge.
A developing roller used in the developing process includes a core made of stainless steel or the like, and a resilient layer formed on the core and made of a resilient material such as silicone rubber or urethane rubber. In order to prevent the contamination and to enhance a quality of printing (for example, a quality of charging), the surface of the resilient layer is processed or coated in consideration of a combination with the toner or other components, as disclosed in Japanese Patent Kokai Publication No. 11-295979 (Pages 2–3, FIG. 1).
However, if the surface of the developing roller is processed or coated, there is a possibility that the surface of the developing roller may be hardened, depending on the condition of processing or coating (for example, a kind or an amount of material to be used) of the developing roller. In a contact-type developing device in which the developing roller contacts the photosensitive drum, the developing roller also contacts a developing blade and a toner supply roller. If the surface of the developing roller is excessively hard, the pressure between the developing roller and contact members (i.e., the developing blade, the toner supply roller and the photosensitive drum) may increase, with the result that a filming may occur.